The distillation properties of liquids and, in particular, petroleum products such as, for instance, fuel are laid down in numerous product specifications. In the case of fuel, it is to be ensured in this manner that engines of the usually occurring capacity and temperature ranges are operated with the appropriate fuels. In this respect, an internationally acknowledged distillation test standard method is available for petroleum products, which is accepted by ASTM and ISO. In that method, 100 ml of the liquid to be analyzed are distilled in a heated distillation flask of glass and condensed in a cooled condenser tube. The condensate is collected in a graduated glass cylinder. Between the onset of boiling and the end of boiling, the temperature of the vapor and the volume condensed up to that point of time are determined (boiling curve). The volume of the distillation residue that remains in the distillation flask after having shut off the heater is determined by the aid of a measuring cylinder, and the boiling curve is corrected accordingly.
That technique was developed around 1920. The control of the heater, the reading of the vapor temperature and the determination of the corresponding condensate volume were carried out by the operator of the device.
U.S. Pat. No. 4,528,635 describes an automatic distillation apparatus. That apparatus employs the same distillation flasks, condensers and glass cylinders as the original, manual method. A device for the determination of the condensed volume as well as a microprocessor controlling heating and cooling and automatically recording measuring data was installed in that apparatus. Basically, the technique remained unchanged though.
That standard technique involves a number of disadvantages for the user. The sample volume is high with 100 ml, the sample and distillation residue have to be dosed and filled manually, the glass flasks and cylinders are fragile and have to be cleaned after every distillation, the measuring time is long, and the apparatus has a large volume and can only be used in laboratories.